Re: Bad use of stringstream temporary?

From:

Victor Bazarov <v.bazarov@comcast.invalid>

Newsgroups:

comp.lang.c++

Date:

Thu, 24 Mar 2011 21:43:30 -0400

Message-ID:

<imgs03$bpa$1@dont-email.me>

On 3/24/2011 8:34 PM, LR wrote:

Victor Bazarov wrote:

On 3/24/2011 3:13 PM, Jeff Flinn wrote:

Victor Bazarov wrote:

On 3/24/2011 12:08 PM, K. Frank wrote:

IIRC,

std::string s = (std::ostringstream()<< std::flush<< "abc").string();

behaves as the OP expected, at least on MSVC8 and gcc4.0.1 under XCode
3.1.2.

You meant .str(), not .string(), I am sure, and yes, it does.
Outputting 'std::flush' (which is a pointer to function) uses a member
op<<, which returns a ref to a non-const stream which then can be passed
to a non-member op<< to output the characters.

Is this certain?

Probably not :-/ My memory must not be as good as it used to be...

I've tried
----------------------------------------------------------------------
#include<sstream>
#include<string>

int main() {
const std::string s
        = (std::ostringstream()<< std::flush<< "abc").str();
}
----------------------------------------------------------------------

Or very similar, with VS2008, GCC 4.5.2 and
http://www.comeaucomputing.com/tryitout/ see below for version, and all
three produced error messages similar to,

-----------------------------------------------------------------------
Comeau C/C++ 4.3.10.1 (Oct 6 2008 11:28:09) for ONLINE_EVALUATION_BETA2
Copyright 1988-2008 Comeau Computing. All rights reserved.
MODE:strict errors C++ C++0x_extensions

"ComeauTest.c", line 5: error: class
           "std::basic_ostream<char, std::char_traits<char>>" has no member
           "str"
   const std::string s = (std::ostringstream()<< std::flush<< "abc").str();
-----------------------------------------------------------------------

LR

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